1. Field of the Invention
The invention relates to a projector apparatus, and in particular, to the light path design of pico projector apparatus.
2. Description of the Prior Art
In recent years, the projection apparatuses usually used by the corporate market are gradually getting into the household market or personal market. For applications of personal portable products, the volume size of projection apparatus and the efficiency of optical engine therein are important issues, and, more particularly, the specific angle of incidence required by the reflection-type image generator built in the projector apparatus needs to be considered to tradeoff between the volume size and the optical engine efficiency.
In order to reduce the size, the pico projector apparatus usually implements design of an LED light source module along with single light path. However, one of the drawbacks is insufficiency of brightness. To enhance the brightness, implementing two (or more) light source modules together with the dichroic combiner forming a single light path could not effectively reduce the volume of apparatus. For instance, the light combination techniques used by U.S. patent application No. US 2006/0279710 A1, US 2006/0164600 A1 or issued U.S. Pat. No. 6,644,814 B2 would result in a larger size of pico projector apparatus. Accordingly, it is desired to provide a pico projector apparatus which satisfy both requirements of smaller size and higher efficiency of optical engine.
To optimize the optical engine efficiency and volume size of pico projector apparatus at the same time, usually the following factors must be balanced: 1. Minimum of light paths, 2. Conjugate imaging of optical design, 3. Minimum folded size of light path.